The present disclosure relates generally to data transmission in mobile communication systems and more specifically to methods for coordinating uplink and downlink communications within a half-duplex communications protocol.
As used herein, the terms “user agent” and “UA” can refer to wireless devices such as mobile telephones, personal digital assistants, handheld or laptop computers, and similar devices that have telecommunications capabilities. In some configurations, a UA may refer to a mobile, wireless device. The term “UA” may also refer to devices that have similar capabilities but that are not transportable, such as desktop computers, set-top boxes, or network nodes.
In traditional wireless telecommunications systems, transmission equipment in a base station transmits signals throughout a geographical region known as a cell. As technology has evolved, more advanced equipment has been introduced that can provide services that were not possible previously. This advanced equipment might include, for example, an enhanced node B (eNB) rather than a base station or other systems and devices that are more highly evolved than the equivalent equipment in a traditional wireless telecommunications system. Such advanced or next generation equipment may be referred to herein as long-term evolution (LTE) equipment, and a packet-based network that uses such equipment can be referred to as an evolved packet system (EPS). As used herein, the term “access device” will refer to any component, such as a traditional base station or an LTE access device, that can provide a UA with access to other components in a telecommunications system.
In mobile communication systems, such as the enhanced universal terrestrial radio access network (E-UTRAN), the access device provides radio accesses to one or more UAs. The access device includes a packet scheduler for allocating uplink and downlink data transmission resources among all the UAs communicating to the access device. The functions of the scheduler include, among others, dividing the available air interface capacity between the UAs, deciding the resources to be used for each UA's packet data transmission, and monitoring packet allocation and system load. The scheduler allocates physical layer resources for downlink shared channel (DL-SCH) and uplink shared channel (UL-SCH) data transmissions, and sends scheduling information to the UAs through a scheduling channel. The UAs refer to the scheduling information for the timing, frequency, data block size, modulation, and coding of uplink and downlink transmissions.
In the latest versions of LTE equipment, two duplexing modes are supported. The first is referred to as time-division duplexing (TDD). When operating in a TDD mode, a common carrier frequency and bandwidth are used to communicate both uplink (UL) and downlink (DL) communications between the UA and the access device. To separate the UL and DL communications, the use of the band is divided in time. For instance, from the UA's perspective, UL communications are restricted to a particular time and duration followed by a predetermined time and duration for receiving DL communications from the access device. To further protect against inadvertent overlapping of UL and DL communications, a guard period (GP) is often employed between UL and DL communication periods. This process of alternating UL and DL communication periods with interspersed GPs continues throughout the communications cycle.
The second duplexing mode is frequency-division duplexing (FDD). In an FDD implementation, distinct carrier frequencies are used for UL communications and DL communications. Accordingly, FDD provides the advantage over TDD of allowing simultaneous transmission of UL and DL communications. However, this advantage comes at the expense of increased hardware complexity, decreased battery life, and increased use of spectrum.
Within the current version of the LTE equipment, there is a third duplexing mode that provides some of the benefits of TDD and FDD. Half duplex (HD) FDD uses separate and distinct carrier frequencies for UL and DL communications, but the communications between the UA and access device are alternated in a manner similar to TDD. As such, battery life is preserved because simultaneous UL and DL communications are avoided and the carrier frequencies, though separate and distinct, could be relatively close together; and in some cases, the only choice due to the spectrum constraints of certain network operators. Further, communications using HD FDD can avoid expensive and complicated duplexer designs that are required within the radio frequency (RF) systems of the UA and access device.
In addition, the current version of the LTE equipment and associated protocols include a number of constraints within which any HD FDD protocol must operate. Referring now to FIG. 1, the frame structure applicable to HD FDD is illustrated. Within this fixed frame structure, the size of various fields in the time domain are expressed on a number of a time unit Ts, which is equal to 1/(15,000*2048) seconds. As illustrated in FIG. 1, DL and UL communications are organized into radio frames 2. Each radio frame 2 is Tf=307200*Ts=10 milliseconds (ms) long and includes a plurality of slots 4 of length Tslot=15360*Ts=0.5 ms, numbered from 0 to 19. A subframe 6 is defined as two consecutive slots where subframe i includes slots 2i and 2i+1. While, as described above, UL and DL communications are separated in the frequency domain, in HD FDD operation using this fixed frame structure, the UA cannot transmit and receive at the same time.
The sub-frames 6 are assigned for UL or DL communication dynamically as a result of the above-described scheduler operation. The UA assumes that any sub-frame 6 not otherwise required for transmission of UL transmission may contain a physical downlink control channel (PDCCH) for assignments of UL and/or DL grants.
When switching between UL transmission and DL reception, the necessary switching time is dictated by the access device. However, when switching between DL reception and UL transmission, the GP is provided at the end of the downlink sub-frame. Thus, for HD FDD operation, the GP is created by the UA by not receiving the last part of a DL subframe immediately preceding an UL subframe from the same UA. Hence, while the length of the reserved period is adjustable with symbol-level granularity and may be cell-specific or associated with the UA-specific timing advance value, the UA will forego receiving at least part of the last DL subframe before a subsequent UL subframe in order to accommodate the GP.
Therefore, it would be desirable to have a system and method to accommodate the GP required to implement HD FDD within the current LTE equipment and associated protocols while addressing the required loss of at least part of the last DL subframe before a subsequent UL subframe to accommodate the GP.